Thanks to the EPA, farmers are not allowed to SPREAD their manure on their crop fields anymore.
I clearly remember growing up on Wisconsin dairy farm & cleaning barns, putting manure into the manure spreader & putting it on the fields.
IF Dad bought any commercial fertilizer, I do not recall such.
I think I was referring to the EPA not allowing Phosphorous mining, not manure spreading. Manure, as well as biosolids from wastewater plants, can be spread under controlled conditions.